When manufacturing a semiconductor device or a liquid crystal display (LCD) panel, photolithography is used for patterning a semiconductor wafer or a substrate for liquid crystal.
In the photolithography, a reticle (referred to as a mask or a masking plate) is used as an original plate for patterning, and a pattern on the reticle is transferred to a semiconductor wafer or an LCD panel. If impurities, such as dust or foreign substances, are adhered to the reticle, light is absorbed in the reticle or reflected from the reticle due to the impurities. Thus, a transferred pattern may be damaged, and accordingly, the performance or yield of a manufactured semiconductor device or LCD panel may be degraded. Accordingly, a pellicle is attached to a surface of a reticle to prevent impurities from adhering to the surface of the reticle.
In this case, even though impurities are adhered to a pellicle formed on the reticle, a light focus is concentrated on patterns of the reticle during lithography, and thus, dust or foreign substances on the pellicle are out of the light focus and thus are not transferred onto the patterns.
The formation of a pattern having a pitch size of 16 nm or less cannot be accomplished by lithography using deep ultraviolet (DUV) light, which is a conventional light source, and needs a light source having a shorter wavelength based on the Rayleigh criterion. Accordingly, lithography using extreme ultraviolet (EUV) light having a relatively short wavelength has drawn attention as the next generation technology with respect to DUV lithography and much research has been performed to develop EUV lithography. However, EUV light having a wavelength of 13.5 nm is considerably absorbed in most materials, and thus, a material that is placed on a path of EUV light in an optical system used in a patterning process is extremely limited, and thus, a material having a very small thickness is required.
A pellicle that has been used for protecting a reticle in a photolithography process is also required in EUV lithography that is still at the research stage, and the development of pellicles is advancing together with the development of an optical system for EUV lithography. Materials, such as Si, Ru, Zr, Mo, and aerogel, have been actively researched as a pellicle film material for EUV lithography.
However, the transmittance of a pellicle with regard to EUV light, which corresponds to a primary condition of a pellicle, is still not satisfied for EUV lithography. To improve the EUV transmittance of a pellicle, a material for the pellicle has to be appropriately selected and the pellicle has to be manufactured to have a very small thickness. However, it is not easy to manufacture a Si, Ru, or Zr film having a very small thickness and maintain its original shape.
In addition, a manufactured pellicle film of a centimeter scale has to have a free-standing ability for the sake of efficient patterning, but a Si, Ru, or Zr film can hardly have a free-standing ability due to a weak tensile strength. Accordingly, researches into a method of supporting a pellicle film by using a mesh formed of Si, Zr, or Ni have been performed (refer to U.S. Pat. No. 8,018,578 B2). However, in this case, due to the mesh, a transmittance of a pellicle film may be reduced and the shape of a projected beam incident thereon may be transformed.